<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>05伪类三角</title>
    <style>
        .box{
            margin: 100px;
        }
        .con{
            /* position: absolute; */
            width: 170px;
            border: 1px #ccc solid;
            box-shadow: 2px 2px 4px rgba(0, 0, 0, .2);
        }

        .con::before{
            /* display: none; */
            content: '';
            width: 0;
            height: 0;
            border: 8px solid #bfa;
            position:absolute;
            top: 120px;
            left: 120px;
            border-style: solid dashed;
            border-color: #fff transparent transparent;
        }
    </style>
    
</head>
<body>
    <div class="box">
        <div class="con">123</div>
        <input type="text" id="jd">

    </div>
    
    
</body>
</html>